They need to know where to point the other merchants and traders for example if there is a problem. Also they needed to know about the technology in that particular area so that the trade can flourish because of that. The environmental effects of migration in the post-classical era could include environmental factors like deforestation, but also effects of languages like assimilation. The linguistic effects of migration in the post-classical era include the spread of languages along trade routes. Trade networks were expanded primarily due to the advancements and growth of empires. The Silk Road was reintroduced with the expansion of the Mongol Empire and many Indian Ocean and African networks became introduced due to the expansion of Islamic power.
Muslim trade networks began in Northern Africa to expand their religion and also to gain riches from the large amounts of gold there. They also created trade networks in the Indian Ocean. But major trade networks began to increase in the Middle East and into Eastern Asia as their empire began to conquer large parts of the Mediterranean. Trade then increased into India as missionaries began to travel to expand